John O'Callaghan is an Irish DJ, mainly producing electronic dance music. He also produces music under the alias of Joint Operations Centre, Mannix and Stenna. He has also collaborated with fellow Discover artists such as Bryan Kearney, Neal Scarborough (as Inertia), Thomas Bronzwaer (as Lost World) and Greg Downey as well as more recently, trance legend Leon Bolier. His best known track is Big Sky, done with vocalist Audrey Gallagher.